usb: gadget: net2280: Move all "ll" registers in one structure

The split into multiple structures of the "ll" register bank is
impractical. It makes it hard to add ll_lfps_timers_2 which is
at offset 0x794, which is outside of the existing "lfps" structure
and would require us to add yet another one.

Instead, move all the "ll" registers into a single usb338x_ll_regs
structure, and add ll_lfps_timers_2 while at it. It will be used
in a subsequent patch.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>